Electrical device casing materials

ABSTRACT

An electrical device; e.g., a transformer, with a fluctuating magnetic field, contained within a casing comprised of steel which has a resistivity in excess of about 65 microhm-cm at room temperature and which is substantially nonmagnetic after a cold reduction of up to 65 percent. The steel consists essentially of up to 0.08% C, up to 2% Mn, up to 1.00% Si, 16.0 - 18.0% Cr, 10.0 - 14.0% Ni, 2.0 - 3.0% Mo, balance Fe and incidental impurities.

United States Patent 1111 3,753,187

Seitanakis Aug. 14, 1973 [54] ELECTRICAL DEVICE CASING 3,301,668 1/1967 Cope 75/128 w MATERIALS OTHER PUBLICATIONS [75] g:. Metals Handbook, Volume 1, page 409, 8th Edition,

8 Published A.S.M., 1961 [73] Assignee: Allegheny Ludlum Industries, Inc.,

P'ttsburgh' Primary Examiner-Hyiand Bizot [22] Filed: May 20, 1971 Att0rney-Richard A. Speer, Vincent G. Gioia et al. 211 App]. No.: 145,484

Related US. Application Data [57] ABSTRACT [62] Division of SCI. NO. 849,610. Aug. 11, 1969, Pat. N0. elecmcal dew; a "ansmmer, 3 3629'761 ating magnetic field, contained within a casing comprised of steel which has a resistivity in excess of about 52 us. C1. 336/90, 75/128 R, 75/128 w 65 microhm-cm at room temperature and which is 51 Int. Cl. 1101: 27/02 S nonmagnetic after a cold reduction of p to 58 Field 61 Search 75/128 w; 336/90 65 Percent The steel con ists essentially of up to 0.08% C, up to 2% Mn, up m 1.00% Si, 16.0 18.0% c1, 10.0

[56] References Cited 14.0% Ni, 2.0 3.0% Mo, balance Fe and incidental UNITED STATES PATENTS mpumles' 1 2,138,754 11/1938 Andrus 336/90 1 Claim, No Drawings excess of 65 microhm cm, preferably in excess of 130 microhm cm, at room temperature; i.e., 68F, and is substantially nonmagnetic; i.e., the. steel has a permeability of less than 1.3, preferably 1.1, at 200 H (oersteds), at cold reductions of up to 65%.

Illustrative casing materials which meet the require-= ments of this invention are given below in Table 1.

TABLE I Composition Feiaind 31 inc ent Alloy -Mn Si Cr Ni N1 M0 A1 impurlties A 0 12-025 14-15.!5v 0.5 16. -18.0 1.00-1. 76 0.32-0.40 Balance, B *0. 2.00 1.00. 10.0-18.0 10.0-14.0 2. 0-3.0 Do. C 015-1 1 -40 10.0 7-16 D0.

' Maximum.

sively heated during operations ofthedevice and more particularly to transformers contained within casings:

comprised of steel which does not become excessively heated during operation of the transformer.

Thealloys of Table 1 differ from the previously used casing materials insofar as they are reliably nonmagnetic; i.e., they are substantially nonmagnetic at cold large transformers,which operateat highcurrent levels;

shows thatv heating is influenced by the second power of current. The second factor is the. eddy currents whose effect is limited by the resistivity. ofthe material. Prior to the present invention, transformer casings;

i.e.,, transformer covers, were comprised of alloys which were presumed'to be nonmagnetic,.such.as A151 type 304 stainless steel and certain manganese nickel iron alloys; e.g., alloys with 10.5 12 .5% manganese, 7 8.5% nickel, balance iron and incidental impurities. 1. have discovered that thosealloys are not reliably non-magneticand are not suitable casings for large transformers; i.e.,.transforrners operating at currents in excess of 10,000 amperes, as they formferromagnetic martensite "whencold: worked.

it is accordingly an object ofthis invention to provide electrical devices with a fluctuating magnetic field con.-

tained .within reliably. nonmagnetic. steel casing materi.

als.

It is an additional object of this-invention toprovide transformers contained within reliably: nonmagnetic steel casing materials.

The article of this invention is an electrical device with a fluctuating magnetic field contained? within a casing comprised of steel. The steel has a resistivity in reductions of up-to 65 percent. Additionally, they minimize the heating caused by eddy currents since they each have a resistivity in excess of 65 microhm cm. at room temperature. Alloy C is preferred over alloys A and B as it has a resistivity at room temperature in excess of microhm cm. A typical. a1loywithin the alloy C range consists. of 0.9 0.95% C, 25-26% Mn, 9-10%A1',.ba1ance iron and incidental impurities. It has a resistivity of about microhm cm.

A. number of cold rolling tests were conducted to demonstrate. the difference. between the casing materials of this invention and those used in the past. Cold rolled were an AlSl type 304 alloy, a manganese nickel ironalloy of the type described above and an alloy which meets the requirements of thisinvention. Typical analyses for these alloysisv given below in Table TABLE 11.

Alloy Composition Fe and incidental C MnCr Ni N, Impurities D 0.08 13518.0 8.5v 8:1 5 0.25 11.50.5 7.25 Bal F 0.18 l5.017.0 1.25 0.35 Bal Alloy D is the type 304 alloy, alloy E is the manganese nickel iron alloy and alloy F is the alloy which meets the requirements of the invention.

Found below in Table 111 are the. results of the cold rolling tests.

TABLE 111 Alloy 1) Alloy E Alloy F 1: Cold (Permeability (Permeability (Permeability Reduction At200-H) At 200 H) At 200 11) 0V 1.015 1.01 1.002 10 1.064 1.32 1.002 30 3.235 1.74 1.003 50 8.480 1.90 1.003 65 14.410 1.95 1.004

The difference in'the casing materials of this invention andthoseused in the past is readily seenfromTable 111. A studyof the results reveals that only alloy F remained substantially nonmagnetic at cold reductions of up to about 65 percent. lts permeability was less than' 1.10 at 200 H (oersteds) after acold reduction of 65 percent. For comparison purposes the. permeability of air is 1.00.- Alloys D and Ebecame somewhat ferromagnetic dueto. the formation ofmartensite. Although the permeability of alloy E is tolerable at low currents and magnetic fields, it is not tolerable at the very high currents and magnetic fields found in the large transformers used today; i.e., transformers of 600 KV and greater. In these large transformers small amounts of ferromagnetism can have a strong influence on case heating. The effect of cold working, exemplified by the above described tests, is compounded by the fact that casings generally undergo the most severe cold working in the area which surrounds the bushings, the area most subject to excessive heating.

It will be apparent to those skilled in the art that the novel principles of the invention diclosed herein in connection with specific examples thereof will suggest various other modifications and applications of the same. It is accordingly desired that in construing the breadth of the appended claims-they shall not be limited to the specific examples of the invention described herein.

I claim: c

1. An electrical device with a fluctuating magnetic field, contained within a casing comprised of steel which has resistivity in excess of about 65 microhm-cm at room temperature and a permeability of less than about 1.3 at 200 oersteds after a cold reduction of up to 65 percent; said steel consisting essentially of up to 0.08% C, up to 2% Mn, up to 1.00% Si, 16.0 18.0% Cr, 1110 72 Ni, ill- 310 71; Mo, balance Fe and incidental impurities; said electrical device being a transformer operable at currents in excess of 10,000 amperes. 

